Method and system for configuring RAID subsystems with block I/O commands and block I/O path

ABSTRACT

A configurable RAID subsystem includes a user data array connected to a user application via a block I/O path, and a configuration array connected to a configuration application via the same block I/O path. The user data array processes user data access commands executed by the user application; and the configuration application processes configuration commands, the user data access commands and the configuration commands communicated to the user data array and the configuration array respectively, via the block I/O path. A dynamic identification is assigned to the user data array by the configuration array, and a static identification is assigned to the configuration array.

FIELD OF THE INVENTION

This invention relates generally to the field of disk storagesubsystems, and more particularly to configuring redundant arrays ofindependent disks (RAID) subsystems.

BACKGROUND OF THE INVENTION

Most modern, mid-range to high-end disk storage subsystems are arrangedas redundant arrays of independent disks (RAID). A number of RAID levelsare known. RAID-1 includes sets of N data disk drives and N mirror diskdrives for storing copies of the data disk drives. RAID-3 includes setsof N data disk drives and one parity disk. RAID-4 also includes sets-ofN+1 disk drives. RAID-5 distributes parity data across all disk drivesin each set of N+1 disk drives.

A RAID subsystem must be configurable. That is, the arrays, whichperform I/O operations for users, must be created, managed, and deleted.Many other functions of the RAID subsystem must also be performed, suchas on-line expansion, RAID level migration, and assigning spare space. Aconfiguration description of the arrays must also be readable, andconfiguration applications must be able to monitor the arrays duringoperation. For that reason, a configuration interface and module areincluded with all RAID subsystems.

FIG. 1 shows components of a computer system 10 including a typicalprior art RAID subsystem 100. The RAID subsystem 100 includes a RAIDconfiguration module 101, and one or more RAID user data arrays 102 eachwith their own array Identification (ID) 104. User applications 111 usea block I/O path 121 to read and write, generally “access,” user data ofthe RAID arrays 102 using the ID 104 assigned to each array. Physically,the RAID arrays 102 store the user data on block storage devices 130.

The problem with the prior art RAID subsystems is that a configurationapplication 110 must use a specialized configuration path 120 tocommunicate with the configuration module 101 to perform theconfiguration functions described above.

FIG. 2 shows the layers of the block I/O path or calling stack 121 usedfor user data transfer. The software and hardware of the block I/O path121 includes, from the top host side to the bottom client side, anoperating system (O/S)—application interface 201, an O/S driverinterface 202, an 1/0 driver 203, a host transport interface 204, an I/Otransport 205, a client or external transport interface 206, a transportdriver 207, and a RAID subsystem interface 208.

The interface 201 translates I/O requests executed by the userapplications 111 for the O/S driver interface 202. The I/O driver 203translates specific O/S calls for the transport layer 205, such as PCI,iSCSI, Infiniband, SCSI, or fibre-optic channel, or some other highbandwidth bus. The transport driver 207 communicates with the RAIDsubsystem interface 208, which in turn communicates with the RAIDsubsystem 100.

The block I/O path 121 is relatively straightforward because mostoperating systems and buses use the same basic functions. Only minordifferences are found among operating system interfaces. Typically, mostof the layers of the stack that form the block I/O path 121 are welldefined. The O/S—application interface 201, the O/S driver interface202, transport interfaces and transport 204-206 are typicallystandardized. Some of the drivers and interfaces may be specialized orproprietary. For instance, most RAID subsystems require a speciallydesigned I/O driver 203, transport driver 207, and RAID subsysteminterface 208.

However as shown in FIG. 3, the layers of the stack that form theconfiguration path 120 generally have far more specialized componentsthan the block I/O path. A configuration interface 301 to theconfiguration application 110 is typically a proprietary set of IOCTLs(I/O control commands) that need to be designed and defined. Aconfiguration driver 302 implements these specialized IOCTLs to allowcontrol of the RAID subsystem 100. The transport layers 303-305, whichalso can use SCSI, fibre, or PCI buses, have specialized block I/Ocommands, and usually the specialized transport interface 303 iscustomized. For SCSI buses, for instance, the transport interface 303uses mode pages with devices. In fact, many RAID subsystems even includea separate third physical path, such as Ethernet, or serial ports toimplement the transport layers 303-305. The driver or external sidetransport interface 305 also uses specialized primitives thatcommunicate with a specialized transport driver 306, and of course aspecialized RAID configuration interface 307.

In all RAID subsystems, the configuration interface 301, configurationdriver 302, host side configuration transport interface 303, client sideconfiguration transport interface 305, transport driver 306 and RAIDconfiguration interface 307 are specialized. Additionally, many RAIDsubsystems even have a specialized configuration transport 304.

Therefore, current RAID subsystems have a severe problem. Theconfiguration portions perform many functions, yet these are notpre-defined. Every operating system requires a re-implementation of theconfiguration functions and interfaces, and every configurationapplication needs specialized software, and perhaps, access tospecialized hardware. This increases the cost and complexity of thecomputer system 10.

Even if the configuration stack 120 were as easy to implement as theblock I/O stack 121, it is still requires a completely separateimplementation to communicate with the configuration module 101. A lotof effort is required to make this possible. In addition, theconfiguration path 120 often has many limitations with respect to thenumber of commands and the amount of information that it can process.

Therefore, there is a need for a RAID subsystem that does not require aspecialized configuration path so that the cost and complexity of theentire computer system can be reduced.

SUMMARY OF THE INVENTION

The invention provides a RAID subsystem that uses only a block I/O pathfor accessing both RAID user data arrays and a configuration array. Aconfiguration application uses the same block I/O path as the userapplication to issue commands to a configuration array, and to receivedata and status in response to these commands.

In fact, to the configuration application, the configuration arrayappears as just another RAID array. The configuration array isdistinguishable from a user array only by its associated configurationarray identification (ID). The configuration array ID enables theconfiguration application to locate the configuration array on the RAIDsubsystem.

Unlike the user data array, the configuration array does not store userdata. Instead, the configuration array receives configuration commands,processes these commands, and supplies the configuration applicationwith configuration information in response to the configurationcommands. The configuration array ID is accessed with block I/Ocommands, and uses block I/O data.

More particularly, a configurable RAID subsystem includes a user dataarray connected to a user application via a block I/O path, and aconfiguration array connected to a configuration application via thesame block I/O path.

The user data array processes user data access commands executed by theuser application, and the configuration array processes configurationcommands. The user data access commands and the configuration commandsare communicated to the user data array and the configuration arrayrespectively, via the block I/O path.

A dynamic identification is assigned to the user data array by theconfiguration array, and a static identification is assigned to theconfiguration array.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art RAID subsystem with a block I/Opath and a specialized configuration path;

FIG. 2 is a block diagram of the layers of the block I/O path of FIG. 1;

FIG. 3 is a block diagram of the layers of the specialized configurationpath of FIG. 1;

FIG. 4 is a block diagram of a RAID subsystem including a configurationarray according to the invention;

FIG. 5 is a flow diagram of the steps performed by the configurationapplication to execute write commands to the configuration array of FIG.4;

FIG. 6 is a flow diagram of the steps performed by the configurationapplication to execute read commands to the configuration array of FIG.4;

FIG. 7 is a flow diagram of the steps performed by the RAID subsystem toprocess configuration write commands according to the invention; and

FIG. 8 is a flow diagram of the steps performed by the RAID subsystem toprocess configuration read commands according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

System Structure

FIG. 4 shows a computer system 40 including a RAID subsystem 400according to the invention. The RAID subsystem 400 includes one or moreuser data arrays 102. A user application 111 accesses the user dataarrays 102 via a block I/O path 121, and the arrays 102 process allblock I/O commands received via the block I/O path 121 from the userapplication 111. The RAID subsystem 400 uses block devices 130, forexample, disk drives, to physically store user data.

The RAID subsystem 400 according to the invention also includes aconfiguration array 401. A configuration application 410 also uses theblock I/O path 121 to access the configuration array 401. In the RAIDsubsystem 400 according to the invention, the configuration array 401appears just like any of the user arrays 102, except for itspredetermined and static configuration identification 402.

Each array 102 exported by the RAID subsystem 400 also has an associateduser identification 104. The dynamic user identifications 104 of theuser arrays 102 are part of the configuration information assigned andprovided by the configuration array 401 that has the staticconfiguration ID 402. The identifications can be stored in a memory ofthe RAID subsystem 400.

With this arrangement, only one set of drivers needs to be implementedfor the application 410 and 111, because all communications with theRAID subsystem 400 are via the single block I/O path 121. That is, theconfiguration application 410 according to the invention uses the samecall stack 121 as the user application 111.

However, the configuration array 401 has a static identification 402,while the user arrays 102 have dynamic identifications 104 that areassigned when the arrays are created by the configuration application410.

Because the block I/O path usually includes a hardware network such asEthernet; or buses such as iSCSI, SCSI, and fibre-optic, theconfiguration application 410 only needs to include primitive I/Ocommand processing for the operating system on which it executes,regardless of whether the RAID subsystem 400 is local or external to thecomputer system.

For an external RAID subsystem, the arrangement according to theinvention is simple to implement. It does not matter what type ofnetwork or bus, internal or external, is used to connect to the RAIDsubsystem 400. All that is needed is the block I/O path 121 withwhatever hardware and software layers that are used to implement it.After the configuration application 410 has determined the configurationID 402, it can direct all configuration commands to the configurationarray 401 via the block I/O path 121, and not via a separate specializedconfiguration path as in the prior art.

User Block I/O Command Execution and Processing

Block I/O user data access commands typically include write and readcommands for specific blocks within the user arrays 102. When a writecommand is processed, the only information that is sent back to the userapplication 111 is a status that indicates whether the command wasprocessed successfully, or not. A read command will also provide userdata. In prior art RAID arrays 102, all commands are processedcompletely independent of each other. That is, the processing of a readcommand is done without any knowledge of a prior write command, forexample. This makes-the-implementation of the configuration array 401using only write and read commands non-obvious.

Configuration Write Command Execution

FIG. 5 shows the steps of configuration write command executionaccording to the invention. In this case, a configuration write commandis assembled 510 by the configuration application 410. Then, theconfiguration application 410 writes to a “block” 520 of the RAIDsubsystem 400 using the block I/O path 121 and the configuration ID 402.The word “block” is used loosely here to emphasize that theconfiguration array 401 appears like any other array to theconfiguration application, although, in fact, it implementsconfiguration functions of a configuration module. After processing thewrite command, the RAID subsystem uses a universally available block I/Ostatus mechanism to return success or failure 530 to the configurationapplication 410.

Configuration Read Command Execution

FIG. 6 shows the steps of configuration read command execution accordingto the invention. In this case, the configuration application 410requests to receive information pertaining to the status or structure ofthe RAID subsystem 400.

To execute a configuration read command, the configuration applicationfirst obtains an application ID. The application ID is used by theconfiguration array 401 to track commands executed by a specificconfiguration application should multiple configuration applications beexecuting concurrently.

Therefore, the configuration application reads a predetermined “block”610 of the configuration array 401, e.g., block 0. When theconfiguration array 401 processes a read command for this block, itreturns a unique application ID for the current configurationapplication 410. From that time on, the configuration array 401 can.track commands executed by that specific configuration application withthe associated application identification.

For subsequent read commands, the configuration application 410assembles 620 a request to read a configuration information datastructure that will convey to the RAID subsystem the specificconfiguration information that is requested. The configurationapplication then writes 630 that request to the configuration array byactually executing a block I/O write for the block with the applicationID. If the return status is error 631, the command is reissued.

Otherwise, if the write command completes successfully 632, theconfiguration application next issues a block I/O read 640 to theconfiguration array 401 to receive the requested information from theRAID subsystem by reading the “block” in the configuration array 401with the number that is equal to the application ID.

The configuration array then uses the application ID to identify therequested configuration information and returns the information withappropriate status 650 to the requesting configuration application.

RAID Subsystem Configuration Array Implementation

The RAID subsystem 400 receives block I/O write and read commands forthe configuration array 401 via the block I/O path 121. Theconfiguration array processes the commands to create or delete arrays inthe RAID subsystem. The configuration array can also perform all othernecessary functions to manage the RAID subsystem, such as, on-lineexpansion, RAID level migration, and assigning spare space. Aconfiguration description of the arrays is also readable, andconfiguration applications can monitor the performance of the userarrays during operation.

Processing Configuration Write Commands

FIG. 7 shows the steps for processing configuration write commandsaccording to the invention. After the configuration array receives ablock I/O write command 710, associated internal data structures withinthe RAID subsystem are locked 720. Typically, these data are locked toprevent multiple configuration applications modifying the same data atthe same time, and also to prevent user access to portions of the userdata arrays while reconfiguration is performed.

The configuration write command is then processed 730 and theappropriate status is set. For example, a new array is created, or anold array is deleted. Then, the data structures are unlocked 740, andthe status is returned 750 to the configuration application.

Processing Configuration Read Commands

FIG. 8 shows the steps for processing configuration read commands. Forthe first use of each application, the application must acquire anapplication ID. The configuration device, will, therefore get a readonce 805 from any new application to the predetermined block thatreturns application IDs. That read will cause a new ID to be generatedand returned to the application.

Next, a configuration read command with a read configuration informationdata structure is received 810 by a block I/O write the configurationarray. This means that the configuration application will subsequentlyalso execute a deferred read command. The specific read command, whichincludes the application ID, is then stored 820 within the RAIDsubsystem.

When the subsequent block I/O read is received 830 by the configurationarray, the block number, i.e., application ID, is compared with anynumber of pending read command/application ID pairs that were stored.When a match pair is found, the appropriate data structures within theRAID subsystem are locked 840, and the requested data are filled 850into the application read buffer. After the read buffer is filled, theRAID subsystem data structures are unlocked 860, and the readinformation is returned 870 to the configuration application along witha return status.

Detailed descriptions of the preferred embodiment are provided herein.It is to be understood, however, that the present invention may beembodied in various forms. Therefore, specific details disclosed hereinare not to be interpreted as limiting, but rather as a basis for theclaims and as a representative basis for teaching one skilled in the artto employ the present invention in virtually any appropriately detailedsystem, structure or manner.

1-18. (cancelled).
 19. A computer program product comprising a computeruseable medium including control logic stored therein for communicatingwith a Redundant Array of Independent Disks (RAID) subsystem comprising:first control logic means for reading user data from and writing userdata to the RAID subsystem via an input/output (I/O) path; secondcontrol logic means for reading configuration information from andwriting configuration information to the RAID subsystem via the I/Opath; wherein the I/O path comprises one or more programs configured tointerface with the RAID subsystem.
 20. The computer program product ofclaim 19, wherein the second control logic means comprises means forexecuting a configuration write command.
 21. The computer programproduct of claim 20, wherein the means for executing a configurationwrite command comprises: means for assembling the configuration writecommand and writing the configuration write command to the RAIDsubsystem.
 22. The computer program product of claim 21, wherein themeans for executing a configuration write command further comprises:means for returning configuration write command status.
 23. The computerprogram product of claim 19, wherein the second control logic meanscomprises means for executing a configuration read command.
 24. Thecomputer program product of claim 24, wherein the means for executing aconfiguration read command comprises: means for obtaining from the RAIDsubsystem an application identification (ID) to be associated with theconfiguration read command.
 25. The computer program product of claim23, wherein the means for executing a configuration read commandcomprises: means for assembling a request to read configurationinformation and writing the request to read configuration information tothe RAID subsystem.
 26. The computer program product of claim 25,wherein the means for executing a configuration read command furthercomprises: means for returning status information regarding writing therequest to read configuration information to the RAID subsystem.
 27. Thecomputer program product of claim 26, wherein the means for executing aconfiguration read command further comprises: means for re-writing therequest to read configuration information to the RAID subsystem if thestatus information indicates an error.
 28. The computer program productof claim 26, wherein the means for executing a configuration readcommand further comprises: means for issuing a configuration read to theRAID subsystem if the status information indicates no error.
 29. Acomputer program product comprising a computer useable medium includingcontrol logic stored therein for controlling a Redundant Array ofIndependent Disks (RAID) subsystem comprising: first control logic meansfor processing user data access commands received via an input/output(I/O) path; second control logic means for processing configurationcommands received via the I/O path; wherein the I/O path comprises oneor more programs configured to interface between the RAID subsystem anda user application that generates the user data access commands and aconfiguration application that generates the configuration commands. 30.The computer program product of claim 29, wherein the second controllogic means comprises means for processing a configuration writecommand.
 31. The computer program product of claim 30, wherein the meansfor processing a configuration write command comprises: means forlocking and unlocking internal data structures of the RAID subsystemassociated with the configuration write command.
 32. The computerprogram product of claim 30, wherein the means for processing aconfiguration write command comprises: means for returning statusinformation pertaining to the processing of the configuration writecommand.
 33. The computer program product of claim 29, wherein thesecond control logic means comprises means for processing configurationread commands.
 34. The computer program product of claim 33, wherein themeans for processing configuration read commands comprises: means forgenerating an application identification (ID) in response to receiving aread for a predetermined block.
 35. The computer program product ofclaim 33, wherein the means for processing configuration read commandscomprises: means for storing a pending configuration read command in theRAID subsystem.
 36. The computer program product of claim 35, whereinthe means for processing configuration read commands further comprises:means for matching a configuration read command with a pendingconfiguration read command stored in the RAID subsystem based on anapplication ID associated with each command.
 37. The computer programproduct of claim 33, wherein the means for processing configuration readcommands further comprises: means for locking and unlocking datastructures in the RAID subsystem associated with a configuration readcommand claim
 38. A computer program product comprising a computeruseable medium including control logic stored therein for communicatingwith a Redundant Array of Independent Disks (RAID) subsystem comprising:first control logic means for reading user data from and writing userdata to the RAID subsystem via a software interface to the RAIDsubsystem. second control logic means for reading configurationinformation from and writing configuration information to the RAIDsubsystem via the same software interface to the RAID subsystem.